Engine starting system using stored energy

ABSTRACT

There is described a method for and system for starting at least one engine from a twin engine installation. The starting system comprises a first engine arrangement comprising a first electric machine having a single rotor dual stator configuration, a first dual channel power control unit coupled to the first electric machine, and a first dual channel full authority digital engine control (FADEC) coupled to the first dual channel power control unit; a second engine arrangement comprising a second electric machine having a single rotor dual stator configuration, a second dual channel power control unit coupled to the second electric machine, and a second dual channel full authority digital engine control (FADEC) coupled to the second dual channel power control unit; an energy storage unit coupled to the first engine arrangement and the second engine arrangement and having at least a first super-capacitor and a second super-capacitor; and a DC to DC converter configured to receive a first voltage level from a power source, increase the first voltage level to a second voltage level, and charge the first super-capacitor and the second super-capacitor to the second voltage level.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 13/803,572, filed Mar. 14, 2013 the content of which is incorporatedherein by reference.

TECHNICAL FIELD

The application relates generally to engine starting systems and moreparticularly, to starting systems based on energy storage devices.

BACKGROUND OF THE ART

Reliability is a critical feature for most vehicles, and particularlyfor aircrafts. In aircrafts, reliability may be improved usingredundancy of components. Should one component fail, a backup isavailable. This strategy, however, causes reliability to be inverselyproportional to desired costs and to desired overall weight. That is tosay, the more redundancy is included in a design, the greater the costsand the greater the weight of the aircraft. As it is also desirable tomaintain both costs and weight relatively low, there is a need forimprovement to aircraft engine systems that would allow reliability tobe increased without negatively affecting costs and weight.

SUMMARY

In one aspect, there is provided an engine starting system for a twinengine installation. The system comprises a first engine arrangementcomprising a first electric machine; a second engine arrangementcomprising a second electric machine; an energy storage unit coupled tothe first engine arrangement and the second engine arrangement andhaving at least a first super-capacitor and a second super-capacitor;and a DC to DC converter configured to receive a first voltage levelfrom a power source, increase the first voltage level to a secondvoltage level, and charge the first super-capacitor and the secondsuper-capacitor to the second voltage level.

In another aspect, there is provided a method of starting at least oneengine of a twin engine installation having a first engine arrangementand a second engine arrangement. The method comprises receiving a firstvoltage level from a power source and increasing the first voltage levelto a second voltage level; charging an energy storage unit having atleast a first super-capacitor and a second super-capacitor to the secondvoltage level; selectively connecting one of the first super-capacitorand the second super-capacitor to a first power control unit in thefirst engine arrangement; controlling a discharge current to a firstelectric machine in the first engine arrangement via the first powercontrol unit; and rotating a rotor of the first electric machine to anabove engine idle speed to start a first engine of the twin engineinstallation.

In yet another aspect, there is provided a method for simultaneouslystarting two engines in a twin engine installation having a first enginearrangement and a second engine arrangement. The method comprisesreceiving a first voltage level from a power source and increasing thefirst voltage level to a second voltage level; charging an energystorage unit having at least a first super-capacitor and a secondsuper-capacitor to the second voltage level; applying power to the firstengine arrangement from the first super-capacitor to start a firstengine; and applying power to the second engine arrangement from thesecond super-capacitor to start the second engine.

DESCRIPTION OF THE DRAWINGS

Reference is now made to the accompanying figures in which:

FIG. 1 shows a schematic cross-sectional view of an example of a gasturbine engine with an electric machine integrated therein;

FIG. 2 is a schematic radial cross-sectional view of an example of anelectric machine;

FIG. 3 is a block diagram of an exemplary starting system for a twinengine installation;

FIG. 4 is a block diagram of an exemplary starting/ignition system foran engine;

FIG. 5 is a flowchart of an exemplary method for starting one enginewith a starting system as per FIG. 3;

FIG. 6 is a flowchart of an exemplary method for starting two enginessimultaneously with a starting system as per FIG. 3; and

FIG. 7 is a flowchart of an alternative embodiment for the method ofstarting two engines simultaneously with a starting system as per FIG.3.

DETAILED DESCRIPTION

There is described herein a starting system for incorporating into anengine having a twin engine installation. FIG. 1 illustrates anexemplary gas turbine (GT) engine for one of the two engines in the twinengine installation. An electric machine 10 driven by a shaft 5 operateswithin the gas turbine engine. Although the illustrated gas turbineengine is a turbofan, the system as described herein can be employedwith a turboprop engine or a turboshaft engine and is not limited toapplication on aircraft engines. The engine may be an aircraft engine, aship engine, a vehicle engine, etc. In alternative embodiments, theelectric machine 10 may be provided in other types of engines, such asan electric engine and a more-electric engine.

The electric machine 10 is operable as either a motor or a generator, orboth, depending on the associated control provided. The materials forthe machine 10 may be any deemed suitable by the designer. Someexemplary materials are samarium cobalt permanent magnets, copper powerand control windings, a suitable saturable electromagnetic material(s)for the stator teeth and power and control flux buses, such as Hiperco50 alloy (a trademark of Carpenter Technology Corporation) may be used,although other suitable materials, such as electrical silicon steelscommonly used in the construction of electromagnetic machines, may alsobe used. The rotor can be ferromagnetic, electromagnetic or a permanentmagnet, and may be provided in an outside or inside configuration, orany other suitable configuration. The stator teeth, power and controlflux buses may be integral or non-integral with one another, as desired.

While machine 10 may have any suitable configuration, in this example itis illustratively a permanent magnet electric machine. FIG. 2 shows anexample of an electric machine 100 described in U.S. Pat. No. 7,262,539,incorporated herein by reference, having two independent channelsections which in essence provide two separately controllable machines,namely machine A and machine B, within the same stator structure 102.The rotor 104 is shown as being outside the stator 102, but it can beinside if desired. Briefly, the stator 102 has a plurality of statorwindings 106 provided in slots 108 of stator 102. Permanent magnets 110are provided on the rotor 104. The channels A, B comprise independentand separated sets of windings 106, and thus machine 100 has atwo-in-one electric machine design. The windings of channel A areconfined to the sector of the stator indicated as “A” in FIG. 2, whilethe windings of channel B are confined to the sector of the statorindicated as “B” in FIG. 2. The windings are independently operable by acontroller, and may be operated each in a motor and generator mode. Forexample, rotation of rotor 104 may be used to generate electricity inthe windings 106 of channel A, while the windings of channel B areturned “off” via the control coils 107 effect on the magnetic propertiesof the stator sector. Alternately, the windings of channel B may also beturned “on” and also used to generate electricity in tandem with thewindings of channel A. The control of the relevant stator, using DCcurrent in the control winding is useful for both controlling thegenerator mode of the machine and the motor mode of the machine. In thegenerator mode of the machine, the DC control current controls the ACoutput current from the windings as is described in U.S. Pat. No.7,262,539. In the motor mode, the control current is normally held at afixed value unless a fault is detected in either the relevant motorwinding or in the relevant motor drive circuit, at which point thecontrol current would be set to zero and the relevant motor drive wouldbe shut off, preventing current generated by the continued rotation ofthe machine from circulating in the fault circuit. The non-failedmotor/motor drive channel is used to continue the rotation of themachine to drive the accessories, while repairs/replacement would bemade at the next earliest opportunity.

The electric machine 10 may be standard or have a dual redundantconfiguration. One exemplary dual redundant configuration is a singlestator dual rotor configuration. Other dual redundant configurations mayalso be applicable, as will be understood by those skilled in the art.The electric machine 10 may also have more than two channels byproviding a single rotor rotating relative to multiple independentstators. In the case of dual channels, the rotor rotates relative to afirst “virtual” stator and also relative to a second “virtual” stator.The electric machine 10 is thus a “two-in-one” machine in this case. Theoutput of these two “machines” may then be combined, which permits theoption of operating the “two machines” as one.

The machine 10 may be single or multi-phase. The windings may havesingle or multi turns per slot, the number of turns of windings does nothave to equal the number of turns of control windings, the number ofturns of a winding does not necessarily have to be a whole number, thenumber of primary windings does not have to equal the number of controlwindings, as one or more windings in a slot may perhaps be present inanother slot. A variety of winding types may be used (squirrel cage,lap, etc.), and the windings may be any conductor(s) (i.e. singleconductor, more than one wire, insulated, laminated, etc.) or may besuperconductors. In multiphase machine, there may be zigzag, delta, orY-connected windings in accordance with known techniques. There need notbe an air gap between the primary and control winding, as long as thewindings are electrically isolated from one another.

Turning now to FIG. 3, there is illustrated an exemplary starting system200 for a twin engine installation, incorporating the electric machine10 described above. In this example, two electric machines 10 operate asstarter-generators 210, 212 and comprises a single rotor 201 dual stator203 configuration. The starter-generators 210, 212 are used for startingthe engines and also generating electricity when the engines are inoperation. Two separate sets of stator windings (Stator A, Stator B) 203are used to drive a common rotor 201 in each starter-generator 210, 212.The two stators 203 each output electricity via their respective sets ofwindings during the generation mode of operation.

The dual channel single rotor starter-generators 210, 212 are controlledby a respective dual channel full authority digital engine control(FADEC) 206, 208 via respective dual channel power control units (PCU A,PCU B) 202, 211. The FADECs 206, 208 may comprise an electronic enginecontroller (EEC) or engine control unit (ECU) and its relatedaccessories in order to control all aspects of engine startingperformance. In particular, the dual FADECs 206, 208 control the inputcurrent to both starter channels of the starter-generators 210, 212based on any one of a number of input parameters, such as speed,temperature, altitude, and forward speed. The FADEC may also control thephase angle of the switching sequence to the motor as a function ofspeed as a means to compensate for phase errors in the motor system

The starter-generator 210, dual FADEC 206 and dual channel PCU 202 forma first engine arrangement for starting the first engine of the twinengine installation. The starter-generator 212, dual FADEC 208 and dualchannel PCU 211 form a second engine arrangement for starting the secondengine of the twin engine installation. An energy storage unit 205 iscoupled to both the first engine arrangement and the second enginearrangement. The energy storage unit 205 comprises at least a firstsuper-capacitor and a second super-capacitor. More than twosuper-capacitors may be provided in the energy storage unit 205. In someembodiments, as illustrated in FIG. 3, the two super-capacitors areelectrical double-layer capacitors (EDLC A, EDLC B). For example, theBoostcap® ultra capacitor from Maxwell Technologies (datasheet BMOD0094P075 B02) with a rated voltage of 75V may be used. Other types ofsuper-capacitors include pseudo-capacitors and hybrid capacitors.

A single DC to DC converter 207 receives a first voltage level from apower source 216 and increases the first voltage level to a secondvoltage level. The power source 216 may take various forms, such as asingle battery, a combination of multiple batteries, a ground powersupply, an engine driven generator, and a rotor driven generator. Thesuper-capacitors are then charged to the second voltage level by the DCto DC converter 207. This allows the super-capacitors in the energystorage unit 205 to be charged to a higher voltage than is typicallyavailable from an aircraft starting supply. For example, thesuper-capacitors may be charged to approximately 72V from a 28V aircraftsupply using a 28V to 72V inverter as the DC to DC converter 207.Charging may take place over an extended period of time, and maintainingthe charge on the super-capacitors requires a relatively small amount ofenergy once the initial charge is completed. In addition, thesuper-capacitors may continue to receive charging current during thestarting process, if desired. Since the charging rate can be orders ofmagnitude slower than the discharging rate during an engine start, thepower source 216 can provide power via a single DC to DC converter 207at a rate which optimizes battery efficiency (in the case of a battery)in terms of its discharge curve. This may allow many more starts from abattery of a given capacity. This may also allow a smaller, and thuslighter, battery to be used.

Each super-capacitor may then be used as a high voltage source toprovide power to one of the engine arrangements, for starting the firstengine and/or the second engine, up to above an idle engine speed. Eachsuper-capacitor of the energy storage unit 205 may be connected directlyto one of the engine arrangements, or alternatively, a switching module,comprising switches 209, 213, may be used to selectively connect thesuper-capacitors to a desired one of the two engine arrangements, thusmaking the super-capacitors interchangeable and capable of startingeither one of the engines. The super-capacitors may be connected to theengine arrangements via the dual channel PCUs 202, 211 instead ofdirectly into the starter-generators 210, 212. This allows the dischargecurrent to the starter-generators 210, 212 to be controlled by the PCUs202, 211 via the dual FADECs 206, 208, respectively, thus maximizing anefficiency of both the starter-generators 210, 212 and thesuper-capacitors.

In some embodiments, an alternate or backup power source 215 may also beprovided. This power source 215 may be any independent power source andmay also be used to feed the energy storage unit 205, for the purposesof charging, recharging, and/or maintaining a charge thereon. It mayalso be provided simply as a redundant power source in case of failureof the primary power source 216. The alternate power source 215 may be,for example, an airframe supplied, transmission mounted generatoroperating at 3.6 KW, 72V, and 50 A. Other types of power sources mayalso be used.

The configuration of FIG. 3 allows the optimization of the startingspeed and acceleration profile, which improves the starting of a gasturbine engine. Dual redundant starting capabilities are also providedfor single engine starting. In addition, both engines of the twin engineinstallation may be started simultaneously, if desired.

Turning now to FIG. 4, there is illustrated en embodiment where thestarting system 200 is used in conjunction with an ignition system 300to start one or both of the twin engines 400. In some embodiments, theignition system 300 is a continuous plasma ignition system, as describedin U.S. Pat. No. 5,587,630, the contents of which are herebyincorporated by reference. Although illustrated as separate, theignition starting system may be incorporated directly into the firstengine arrangement and the second engine arrangement, such that aseparate continuous plasma ignition system is used for lighting each oneof the engines in the twin engine installation. Alternatively, a singlecontinuous plasma ignition system is used for both engine arrangements,in a switchable configuration.

In some embodiments, the ignition system 300 comprises a dual redundantconfiguration, similarly to the starting system 200. For example, dualignition exciters, dual air gap ignitors and dual sets of electricallyshielded cables to interface the exciters are provided for each ignitionsystem 300. In the case of one ignition system 300 per engine of thetwin engine configuration, an ignition system 300 with dual redundantconfiguration is provided for each engine arrangement 210, 212.Alternatively, one dual redundant ignition system is switchable betweenthe first engine arrangement 210 and the second engine arrangement 212.

FIG. 5 illustrates an exemplary method of starting at least one engineof a twin engine installation having a first engine arrangement and asecond engine arrangement. As depicted in FIG. 3, each enginearrangement may comprise, but does not require, an electric machine witha single rotor dual stator configuration operating as astarter-generator, a dual channel PCU, and a dual FADEC. In a first step502, a first voltage level is received from a first power source. Thefirst voltage level is increased to a second voltage 504 and used tocharge an energy storage unit with at least two electrically separatesuper-capacitors 506. At least one of the two super-capacitors isselectively connected to the PCU of one of the engine arrangements 508and current is controllably discharged through the PCU to the electricmachine 510. At least one of the twin engines is thus started byrotating a rotor of the electric machine to an above engine idle speed512.

As indicated above, the first voltage level may be received from any oneof a single battery, a plurality of batteries, a ground power supply, anengine driven generator, and a rotor driven generator. Should it bedesired to use the second super-capacitor to start the first engine, itmay be switched from the second engine arrangement to the first enginearrangement.

FIG. 6 illustrates an exemplary method for concurrently starting bothengines of a twin engine installation. Once the energy storage unit hasbeen charged to a second voltage level greater than the first voltagelevel as received, one super-capacitor is connected to the PCU of thefirst engine arrangement 508 while the other super-capacitor isconnected to the PCU of the second engine arrangement 509. Dischargecurrent is controlled independently to each one of the first electricmachine and the second electric machine via their respective PCUs 510,511. Each engine is started by rotation of a rotor of a respectiveelectric machine, 512, 513.

As illustrated in FIG. 7, the method may also comprise a step ofrecharging/maintaining the charge on the energy storage unit 505. Thismay be done by the DC to DC converter or by the alternative or backuppower source. The engine(s) may also be lit using one or more of therespective continuous plasma ignition systems 507.

While illustrated in block diagrams as groups of discrete componentscommunicating with each other via distinct data signal connections, itwill be understood by those skilled in the art that the presentembodiments may be provided by a combination of hardware and softwarecomponents, with some components being implemented by a given functionor operation of a hardware or software system, and some of the datapaths illustrated being implemented by data communication within acomputer application or operating system. For example, the power controlunits 202, 211 may be implemented using hardwired logic,Field-Programmable Gate Arrays (FPGAs), analog systems, etc. Thestructure illustrated is thus provided for efficiency of teaching of thepresent embodiment, which can be carried out as a method or embodied ina system. The above description is meant to be exemplary only, and oneskilled in the art will recognize that changes may be made to theembodiments described without departing from the scope of the inventiondisclosed. Modifications which fall within the scope of the presentinvention will be apparent to those skilled in the art, in light of areview of this disclosure, and such modifications are intended to fallwithin the appended claims.

1. An engine starting system for a twin engine installation comprising:a first engine arrangement comprising a first electric machine; a secondengine arrangement comprising a second electric machine; an energystorage unit coupled to the first engine arrangement and the secondengine arrangement and having at least a first super-capacitor and asecond super-capacitor; and a DC to DC converter configured to receive afirst voltage level from a power source, increase the first voltagelevel to a second voltage level, and charge the first super-capacitorand the second super-capacitor to the second voltage level.
 2. Theengine starting system of claim 1, wherein at least one of the firstengine arrangement and the second engine arrangement comprises a dualredundant configuration.
 3. The engine starting system of claim 2,wherein the dual redundant configuration comprises a single rotor dualstator configuration for the electric machine, a dual channel powercontrol unit, and a dual channel full authority digital engine control(FADEC) coupled to the dual channel power control unit.
 4. The enginestarting system of claim 1, further comprising a switching unitoperatively connected between the energy storage unit, the first enginearrangement and the second engine arrangement and configured forselectively connecting the first super-capacitor and the secondsuper-capacitor to the first engine arrangement and the second enginearrangement.
 5. The engine starting system of claim 1, wherein the firstengine arrangement comprises a first continuous plasma ignition systemand the second engine arrangement comprises a second continuous plasmaignition system.
 6. The engine starting system of claim 1, furthercomprising a backup power source that is transmission mounted andcoupled to the energy storage unit, for at least one of recharging andmaintaining a charge on the first super-capacitor and the secondsuper-capacitor.
 7. A method for simultaneously starting two engines ina twin engine installation having a first engine arrangement and asecond engine arrangement, the method comprising: receiving a firstvoltage level from a power source and increasing the first voltage levelto a second voltage level; charging an energy storage unit having atleast a first super-capacitor and a second super-capacitor to the secondvoltage level; applying power to the first engine arrangement from thefirst super-capacitor to start a first engine; and applying power to thesecond engine arrangement from the second super-capacitor to start thesecond engine.
 8. The method of claim 7, further comprising: controllingcurrent discharge to a first electric machine in the first enginearrangement by applying power from the first super-capacitor via a firstpower control unit; and controlling current discharge to a secondelectric machine in the second engine arrangement by applying power fromthe second super-capacitor via a second power control unit.
 9. Themethod of claim 7, further comprising connecting the firstsuper-capacitor to the first engine arrangement and connecting thesecond super-capacitor to the second engine arrangement.
 10. The methodof claim 7, wherein receiving the first voltage level from a powersource comprises receiving the first voltage level from a singlebattery.
 11. The method of claim 7, further comprising at least one ofrecharging and maintaining a charge on the first super-capacitor and thesecond super-capacitor using a backup power source that is transmissionmounted.